New engine adaptations and designs are being studied and developed to attempt to improve the traditional combustion process, mainly the four stroke combustion system. Some examples of the adaptations are revisions in carburation techniques, fuel consumption monitoring, alterations in combustion chamber aerodynamics, basic engine configurations such as the rotary engine, vaporization and ionization of fuel for more complete combustion, new exotic fuels, and other processes. While these are all worthwhile endeavors and knowledge is gained through these efforts, the basic problems are not solved and the basic variables of these engines' operation are not fully coordinated.
In all engines there are four fundamental variables that must be worked with in various ways so they complement each other to produce desirable results. These variables are time and temperature of combustion, density of the gas and area of the combustion chamber. The desirable results are complete combustion with a relatively low exhaust temperature. Density is the easiest variable to manipulate through adjustments in liquid flow. The other three are more difficult.
At a given temperature there must be sufficient time to complete combustion. The lower the temperature the longer the time for complete oxidation. The higher the temperature the shorter the time for oxidation. This temperature variable has certain upper and lower limits. A temperature of 3200 degrees C. appears to be the upper limit of combustion without NO.sub.2 formation in an unrestricted environment, and 5500 degrees C. is the highest temperature achievable by a chemical reaction.
A measure of efficiency of an engine is the relationship between the highest temperature allowed minus the output temperature of exhaust divided by the first temperature. Therefore it is impossible here on earth to get an absolutely efficient temperature relationship because the exhaust temperature can never be below outside air temperature. To be at top efficiency the exhaust temperature would have to be absolute zero. The six cycle configuration takes care of these temperature limitations.
Temperature also has a relationship with pressure. This relationship is dependent on the density of the gas involved; temperature being a measure of the average kinetic energy of the gas. A gas with low density can have molecules with very high velocity and still have low pressure, but this same gas with high density and the same velocity would have high pressure and a high temperature. The average kinetic energies of the high and low density examples are the same; only their densities and pressures have changed. These variables can be switched around to achieve similar results along different paths.
The time of combustion is just as critical as temperature to achieve the desirable result of total oxidation and extraction of energy from a given unit of fuel. Given the limits of temperature there is just not enough time in present engine designs to give complete oxidation no matter what the mixture setting. The time to oxidation ratio gets even worse as increases of throttle and power settings are offset by higher rpm's due to the relatively unchanging size of the combustion chamber. It may be somewhat better under load conditions.
A continuous time of oxidation is probably ideal, such as presented in steam and turbine engines, but they have problems with the other variables, e.g. area and heat transfer, density and disassociation. They also have mechanical limitations of valving, power strokes related to rmp, heat resistent materials, and lubrication breakdown at extreme temperatures and exposure to the products of combustion (silicone based oils). The variable of time is also handled by the six cycle configuration.
Increasing the amount of time in a combustion chamber involves increasing the surface area of the chamber. The ratio of volume to area in a sphere or even a cylinder is a disproportionate one. Increasing the volume of space enclosed by a sphere or cylinder by a unit does not increase the surface area of that enclosure by the same unit, but by a fraction of a unit. Any surface area is detrimental to some extent. The kinetic energy of the molecules is diminished when they touch this surface.
When time is increased, oxidation is enhanced, but surface area is increased and heat loss is increased. This is at the heart of the problems involved in engine designs, internal and external. The question is "How are the fuel, oxygen and combustion products, and their kinetic energy and velocity separated from the surface area of the combustion chamber?" "How are they to be insulated inside the chamber?"